1. Field of the Invention
The present invention relates to a collision type decision device for deciding whether a vehicle has had a head-on (symmetric) collision or an asymmetric collision.
2. Description of the Background Art
A driver/passenger protection apparatus, e.g., air bag, on a vehicle is controlled to activate by a protection activation device. Conventionally, the human protection activation device detects an impact on the vehicle as a deceleration by means of an acceleration sensor, and controls the activation of the human protection apparatus on the basis of the measured deceleration.
There are various collision types including a symmetric (full-wrap) collision where the entire front face of a vehicle is impacted, an asymmetric (offset) collision where a part of the front face of a vehicle is impacted, and a bias collision where a vehicle is impacted by a skewed force having a certain angle. In order to activate a suitable human protection apparatus at more appropriate timing, the use of a collision type decision device has been contemplated.
JP-A-2000-255373 discloses collision type decision devices, each of which decides the collision type by means of acceleration sensors (satellite sensors) situated at the left and right front corners of a vehicle. One of the collision type decision devices disclosed in the publication calculates the respective velocity values of the left and right portions of the vehicle on the basis of the measured decelerations, recognizes the time moments when the respective velocity values exceed a threshold, and decides the collision type on the basis of the time difference between the time moments.
Another collision type decision device disclosed in the publication decides the collision type on the basis of the difference between the left and right velocity values of the vehicle. A still another collision type decision device identifies the time moments when the respective velocity values reach respective peaks and decides the collision type on the basis of the difference between the time moments. These devices utilize a theory that either of the left and right acceleration sensors produces a larger output when an asymmetric collision occurs.
FIG. 16 is a block diagram showing in a simplified form one of collision type decision devices disclosed in JP-A-2000-255373. In FIG. 16, numeral 520 designates a collision type decision device. The collision type decision device 520 includes a left front sensor 22, a right front sensor 24, an arithmetic unit 530, and a comparison unit 540. The sensors 22 and 24 that are disposed left and right front corners of a vehicle, respectively, detect the accelerations (more exactly, decelerations) at the respective positions. The arithmetic unit 530 makes calculations on the outputs of the sensors 22 and 24 to obtain respective arithmetic results with respect to the left and right portions of the vehicle and calculates the difference between the arithmetic results. For example, the arithmetic unit 530 integrates the respective outputs Gl and Gr of the left and right sensors 22 and 24 to obtain the left and right velocities f(Gl) and f(Gr) and calculates the velocity difference |f(Gl)xe2x88x92f(Gr)|. The comparison unit 540 compares the velocity difference |f(Gl)xe2x88x92f(Gr)| with a threshold Thr0 and decides the collision type on the basis of the comparison result.
Conventionally, the left and right front acceleration sensors 22 and 24 are located near the engine room. Accordingly, the temperature change resulting from that in the engine room and other disturbances may affect the acceleration sensors 22 and 24, thereby frequently disenabling the decision device to decide the collision type properly. For example, if either of the left and right acceleration sensors 22 and 24 is significantly affected by the temperature change in comparison with the other sensor although the vehicle has had a symmetric collision, the collision type decision device may improperly decides that an asymmetric collision has occurred.
This problem will be discussed in more detail with reference to FIGS. 17A and 17B. FIG. 17A depicts results at a symmetric collision while FIG. 17B depicts results at an asymmetric collision. In these graphs, dotted lines depict results when no disturbances were applied to the sensors while solid line depict results when some disturbances were applied to the sensors. As will be understood from the dotted lines in FIG. 17A, at the symmetric collision, the velocity difference |f(Gl)xe2x88x92f(Gr)| was always lower than the threshold Thr0. As in FIG. 17B, at the asymmetric collision, the velocity difference |f(Gl)xe2x88x92f(Gr)| exceeded the threshold Thr0 at at least a certain period.
However, as will be understood from the solid lines in FIG. 17A, even at the symmetric collision, when some kind of disturbance was applied, the velocity difference |f(Gl)xe2x88x92f(Gr)| increased farther than that at no disturbance and exceeded the threshold Thr0 for any while. Furthermore, although the same disturbance was applied while the asymmetric collision has occurred, the velocity difference |f(Gl)xe2x88x92f(Gr)| might decrease to be lower than that at no disturbance and be always lower than the threshold Thr0 as will be understood from FIG. 17B. These phenomena make appropriate decisions difficult, so that it is difficult for manufacturers of collision type decision devices to even set the threshold Thr0.
Accordingly, it is an object of the present invention to provide a collision type decision device for making appropriate decisions of collision type although there are measurement errors of sensors resulting from disturbances.
In accordance with an aspect of the present invention, a collision type decision device includes left and right deceleration detectors, an average calculating unit, and a decision unit. The left and right deceleration detectors are located at left and right front portions of a vehicle for detecting decelerations at the left and right front portions, respectively. The average calculating unit calculates an average of values based on the decelerations detected by the left and right deceleration detectors. The decision unit compares the average with a threshold and decides whether a collision type of the vehicle is a symmetric or asymmetric on the basis of the comparison.
With such a structure, it is possible to make appropriate decisions of collision type although there are measurement errors of deceleration detectors resulting from disturbances.
In an embodiment, the collision type decision device may further include an arithmetic unit for calculating the decelerations detected by the deceleration detectors to obtain arithmetic results with respect to the left and right portions of the vehicle. The average calculating unit may calculate an average of the arithmetic results.
With such a structure, the arithmetic unit may obtain left and right velocities, jerks, and other optional arithmetic results. The collision type decision device can make appropriate decisions of collision type on the basis of such optional arithmetic results.
In another embodiment, the average calculating unit may calculate an average of the decelerations themselves detected by the left and right deceleration detectors.
With such a structure, it is possible to make appropriate decisions of collision type in a more simplified manner.
The collision type decision device may further include a central deceleration detector located near the central portion of the vehicle for detecting deceleration at the central portion, and a collision beginning detector for detecting a collision beginning moment of the vehicle on the basis of the deceleration detected by the central deceleration detector or on the basis of the decelerations detected by the central deceleration detector and at least one of the left and right deceleration detectors. The decision unit may output the decision result thereof for only a certain period after the collision beginning moment.
With such a structure, the device may utilize a great deceleration, which may inherently occur at the initial impact stage after a symmetric collision, as a key, and may discriminate symmetric collisions from asymmetric collisions readily, precisely, and quickly.
In another embodiment, the collision type decision device may further include a central deceleration detector located near the central portion of the vehicle for detecting deceleration at the central portion. The decision unit may compare the threshold with a change in the average calculated by the average calculating unit for a period before a value based on the deceleration at the central portion reaches a certain level, may decide whether a collision type of the vehicle is a symmetric or asymmetric on the basis of the comparison, and may output no decision on the collision type of the vehicle based on the left and right decelerations after the value based on the deceleration at the central portion reaches the certain level.
With such a structure, the device may ignore the peak of the selection result at the posterior impact stage after an asymmetric collision without using a trigger for detecting a collision beginning moment of the vehicle. Therefore, the device may utilize a great deceleration, which may inherently occur at the initial impact stage after a symmetric collision, as a key, and may discriminate symmetric collisions from asymmetric collisions readily, precisely, and quickly.
In this case, the collision type decision device may further include a second arithmetic unit for calculating the deceleration detected by the central deceleration detector to obtain an arithmetic result with respect to the central portion of the vehicle. The decision unit may utilize the arithmetic result with respect to the central portion as the value based on the deceleration at the central portion.
With such a structure, the second arithmetic unit may obtain the central velocity, jerk, and another optional arithmetic result. The collision type decision device can make appropriate decisions of collision type on the basis of such an optional arithmetic result.
In another embodiment, the decision unit may utilize the deceleration itself detected by the central deceleration detector as the value based on the deceleration at the central portion.
With such a structure, it is possible to make appropriate decisions of collision type in a more simplified manner.
The decision unit may output a decision result on the collision type of the vehicle, which is based on the left and right decelerations before the value based on the deceleration at the central portion reaches the certain level, after the value based on the deceleration at the central portion reaches the certain level.
With such a structure, it is possible to freely set an initial condition, such as the threshold for controlling the activation of a driver/passenger protection apparatus, at the initial stage after a collision.
In accordance with another aspect of the present invention, a collision type decision device includes left and right deceleration detectors, a selecting unit, and a decision unit. The left and right deceleration detectors are located at left and right front portions of a vehicle for detecting decelerations at the left and right front portions, respectively. The selecting unit selects a lower value between two values based on the decelerations detected by the left and right deceleration detectors. The decision unit compares a selection result selected by the selecting unit with a threshold and for deciding whether a collision type of the vehicle is a symmetric or asymmetric on the basis of the comparison.
With such a structure, it is possible to make appropriate decisions of collision type although there are measurement errors of deceleration detectors resulting from disturbances.
In an embodiment, the collision type decision device may further include an arithmetic unit for calculating the decelerations detected by the deceleration detectors to obtain arithmetic results with respect to the left and right portions of the vehicle. The selecting unit may select a lower arithmetic result among the arithmetic results.
With such a structure, the arithmetic unit may obtain left and right velocities, jerks, and other optional arithmetic results. The collision type decision device can make appropriate decisions of collision type on the basis of such optional arithmetic results.
In another embodiment, the selecting unit may select a lower deceleration among the decelerations themselves detected by the deceleration detectors.
With such a structure, it is possible to make appropriate decisions of collision type in a more simplified manner.
In an embodiment, the collision type decision device may further include a central deceleration detector located near the central portion of the vehicle for detecting deceleration at the central portion. The decision unit may compare the threshold with a change in the selection result selected by the selecting unit for a period before a value based on the deceleration at the central portion reaches a certain level, may decide whether a collision type of the vehicle is a symmetric or asymmetric on the basis of the comparison, and may output no decision on the collision type of the vehicle based on the left and right decelerations after the value based on the deceleration at the central portion reaches the certain level.
With such a structure, the device may ignore the peak of the selection result at the posterior impact stage after an asymmetric collision without using a trigger for detecting a collision beginning moment of the vehicle. Therefore, the device may utilize a great deceleration, which may inherently occur at the initial impact stage after a symmetric collision, as a key, and may discriminate symmetric collisions from asymmetric collisions readily, precisely, and quickly.